In current broadcast television systems a picture or frame, is composed of two fields which are generated and transmitted sequentially in time. This method of image scanning and display is termed interlaced scanning. Interlaced scanning has various benefits, one of which is a reduction of large area image flicker which results from the presentation of each image twice per picture. However, since the two fields are off set in time, possibly by generation and certainly by transmission, artifacts are produced at vertical transitions within the displayed image. For example, an edge of a vertical transition will be portrayed by a line, or part thereof, from a single field. Thus the edge of the vertical transition is described by a signal which is present once per picture, or frame. Hence, due to the luminous decay of the display phosphor, the edge will diminish in brightness before re-illumination in the next frame. Thus, for the edge line, the interlacing process fails to raise the image display rate beyond that of human visual perception with the result that the edge defining line flickers in brightness at picture rate.
It is known that the visibility edge or line flicker may be reduced by adaptive modulation of the vertical deflection field. However, the deflection amplifier employed for such adaptive modulation requires the use two control signals. A first signal defines modulation magnitude and a second signal which controls a bridge configuration to determine deflection direction. It is desirable that an amplifier for adaptive modulation of the vertical deflection field be simplified to be responsive to a single control signal which is indicative of both magnitude and direction.